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E. T. GREENFIELD. TUBE POR ELECTRIC GONDUGTORS. I

Patented Feb., 23, 1892.

(No Model.)

UNITED STATES PATENT OFFICE.

EDVIN T. GREENFIELD, OF NEV YORK, N. Y., ASSIGNOR TO THE INTERIOR OONDUITAND INSULATION COMPANY, OF SAME PLACE.

TUBE FOR ELECTRIC CONDUCTORS.

SPECIFICATION forming part of Letters Patent No. 469,469, dated February 23,1892.

Application iiled March 2l, 1891. Serial No. 385,389. (No model.)

T0 all whom it may concern.-

Be it known that I, EDWIN T. GREENEIELD, a citizen of the United States, residing at New York, in the county and State of New York,

, have made a new and useful Improvement in Insulated Ooncentric Tubes for Use in Connection withElectrical Conductors, of which the following is a specification.

My invention is directed particularly to a novel method of constructing compound concentric tubes in which the tubes are separated from each other by insulating material; and it has for its objects, first, the preparation of a tube of this compound character which may be completed as an article of manufacture; second, the preparation of such a compound tube and in such manner that the tubes may be absolutelyconcentric at all points of theirlength and be thoroughly insulated from each other; third, the adaptation of means for preventing the tubes from coming into contact with each other after they have once been united by the insulating material which separates them, and, fourth, the construction of a compound conduit-tube, the inner tube being made of paper or analogous fibrous material treated with waterproofing material, the outer tube being of iron, phosphorrbronze, or some substance not readily attacked by acids or alkalies, said tubes being joined to@L gether by an insulating compound. I accomplish these several objects by the practice of the methods and the use of the compound tube hereinafter described, but particularly pointed out in the claims which follow this speoiiication.

My invention will be fully understood by referring to the accompanying drawings, in which- Figure l represents a side elevational view of one of the inner tubes, showing one end partially broken away and stopples in either endthereof, together with a cord or rope wound spirally around it and held in place by the Prior to my present invention it was old in the art to locate tubular conduits or ducts made of iron, prepared paper, and various kinds of material in a conduit having a removable cover and to properly space said ducts or conduits with spacing-blocks, after which the conduit was filled with molten pitch or some analogous bituminous insulating product, and the material allowed to set or harden about the ducts or tubes, thereby firmly uniting them to each other and to the conduit and insulating them therefrom. It was also old in the art to lay tubes made of paper or analogous fibrous material previously treated with insulating material directly in the ground, or to locate tubes of this nature in the walls of buildings and cement conduits in places they `were liable to be attacked by acids and alka- 'Conlies, which rapidly decompose them. centric conduit-tubes made of various kinds of material and permanently united by an insulating compound were also old prior to my invention.

Vhile the present invention is directed,

broadly, to a novel method of constructing compound tubes insulated from each other by a fixed or setinsulation, which spaces them equally at all points of their length, it is also directed specically to a novel method of constructing a compound tube, the inner one of which is of treated or prepared paper or analogous iibrous material protected by a su rrounding concentric tube not easily attacked by acids or alkalies, said tubes being joined together by a iixed or set insulating material and maintained at equal distances apart throughout their length by a spirally-arranged spacing device, and my claims hereinafter made are designed to cover also this specific construction.

Referring to the drawings in detail, IJ represents the exterior tube preferably screwthreaded at both ends and provided with a removable screw-threaded cap C.

P represents the inner or concentric tube, made, preferably, of treated paperand of somewhat smaller diameter than the inner diameter of the exterior tube. Around this inner tube P', I wind in spiral form a rope or cord A, preferably of tarred hemp, and firmly secure the ends thereof in the inner ends of the tube by a pair of stopples D D', said stopples being provided with grooves adapted to receive ICO Y position above described.

the inward-projecting ends of the cord, as clearly shown at the right-hand end of Fig. 1. The exterior or projecting portion of the stopple D is of substantially the same length as the distance between the bottom of the cap C and the end of the tube P, so that when the inner tube is forced fully home the ends of both tubes will lie in the same plane, as clearly shown in Fig. l. The outer tube P is then placed vertically and a molten insulating material-such as pitch or any well-known analogousinsulating material-poured into it until it is partially filled, the amount of the material being preferably such as will fill the inner space between the tubes when the in ner tube is forced downward, so that the stopple D rests upon the bottom of the cap C. Vhilethe insulating material is in this liquid condition, I insert the interior tube P', after the manner shown in Fig. 3, and force it downward until the stopple D assumes the The act of thus forcing the inner tube inward causes the molten insulating material to be forced upward around the spiral convolutions of the centering-cord A, this cord being of such diameter as to substantially iill the space between the tubes. thus forced home I allow the insulating material to cool or set, or I may hasten this setting process by chilling 'the tube with water or in any other preferred manner, after which the cap C is unscrewed and the stopplesD D removed, the solid or set insulating' material between the tubes being a medium for fixedly uniting them together. The completed tube will appear as shown in Fig. 4, and for the purpose of conduit use these sections of tubing may be joined together end to end by collars fitting over the screw-threaded portions S, after the manner of joining gas, water, or analogous pipes. It will be seen, also, that the spacing-cord A will prevent the tubes from ever coming into actual contact with each other, no matter to what temperature they maybe subj ected-a feature which is particularly desirable where conduits or ducts come into close proximity to steam-pipes or analogous heated surfaces.

I do not limit myself to the practice of the improved methods hereinafter claimed for making conduit ducts or tubes alone, as it is obvious that I may practice said methods in the insulation of conductors by inserting a conductor wound with a spacing device inside of a tube filled with a molten materialI in the manner described and claimed.

It will also be understood that I do not limit myself to the tubes of cylindrical crosssection, as I may use tubes of any cross-section as of rectangular or polygonal form.

It is apparent that when the insulating material is poured into the tube in molten condition, in the manner shown in Fig. 3, the entire exterior tube is heated and the mass of molten insulating material is of such quantity that in its liquid conditionit will rapidly After the inner tube isl Vend of the tube when the two are in their fixed position and be sure that it will penetrate all of the space between the two tubes.

Having thus described my invention, what I desire to secure by Letters Patent of the United States is- 1. The described method of insulating concentric tubing, consisting in partially filling the outer tube with insulating material in Aliquid form, then inserting the inner tube,

thereby causing the insulating material to fill the space between the two, and nally causing or allowing the insulating material to harden or set, whereby the tubes are firmly united together, substantially as described.

2. The described method of making an insulated conduit, consisting in partially filling a tube with liquid insulating material, then inserting a second tube closed at the inserted end, thereby causing the insulating material to be forced between the two tubes, and finally causing or allowing the insulating material to harden or caset, so as to rmly bind said tubes together, substantially as described.

3. The described method of insulating concentric tubes, pipes, or conductors, consisting in partially filling one tube with liquid insulating material, then forcing a second closed tube of smaller diameter into the first tube, thereby causing the' insulating material to separate the two, and finally allowing or causing the insulating material to harden or set, substantially as described.

4. The described method of insulating concentric tubes, consisting in first surrounding the smaller tube with a spacing device, then filling the outer tube partially with insulatr ing material in a liquidstate, then forcing the smaller tube into the larger, so that the two are entirely separated by the liquid, and finally allowing or causing the insulating material to harden orset, substantially as described. Y

5. The described method of insulating concentric tubes, consisting in temporarily closing one end of each tube and winding a spiral cord about the smaller, then partially filling the larger with a liquid insulating medium, then forcing the closed end of the smaller tube into the larger until it reaches the closed end thereof, and allowing or causing the insulating material to chill or set, substantially as described.

EDWIN T. GREENFIELD.

Witnesses: A

G. J. KINTNER, M. L. BUTLER.

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